UNI- AND MULTI-NUCLEATE CELLS 59 



cells the streaming movements which continually convey new portions of 

 cytoplasm to the close neighbourhood of the nucleus are of considerable 

 importance, as indeed any changes in the form or position of the nucleus 

 itself may also be. 



It is, for example, often the case that the nucleus is found in the 

 neighbourhood of the point at which the growth of the cell-wall is most 

 active 1 . This is not, however, always the case, for the nucleus in the root 

 hairs of Trianea bogotensis, probably for mechanical reasons, remains 

 at the broadened base of the root hair, and not at the apex where growth 

 in length is active 2 . 



The plasmatic threads which pass through the walls of the contiguous 

 cells of a tissue unite the different protoplasts together, and thus ensure 

 the harmonious co-operation of the whole by allowing each protoplast 

 to communicate with and interact with its neighbours 3 (Sect. 4). The 

 existence of protoplasmic continuity renders it possible that single 

 elementary organs, as for example sieve-tubes *, may exist and show vital 

 activity without possessing a nucleus of their own, while in order that 

 cilia may remain active, a living intracellular connexion must exist between 

 them and the nucleated protoplast 5 . 



By this intercellular protoplasmic continuity, the protoplasts of multi- 

 cellular plants are bound together to form a concrete whole. Hence it is 

 impossible to lay down any hard and fast line of demarcation between 

 multicellular and unicellular multinucleate plants, especially as the 

 plasmatic connexions in multicellular plants show all grades of transition 

 from the finest threads to coarse strands. Indeed, in some cases, as for 

 example in Cladophora, the formation of the transverse partition walls 

 may be partially suppressed under certain conditions. The segmentation 

 of the organism into cells is of importance in many respects, for it ensures 

 a sufficiently firm and rigid structure, and at the same time provides 

 suitable dwelling-places for the soft-bodied protoplasts (Sect. 6). More- 

 over, local injuries are less dangerous than in large unicellular plants, 

 while the varied forms and contents of the cells directly demonstrate what 

 a marked differentiation of labour is possible between the component cells 



1 [Haberlandt, Beziehungen zwischen Function und Lage des Zellkernes, 1887.] 



2 Fig. in Unters. a. d. Bot. Inst. z. Tubingen, 1886, Bd. n, Taf. ii, Fig. 5. See also Pfeffer. 

 1896, Ber. d. Sachs. Ges. d. Wiss., p. 505. 



3 On plasmatic threads and their mode of formation, see the reference by Zimmermann, Beihefte 

 z. Bot. Centralbl.. 1893, Bd. in, p. 328; A. Meyer, Bot. Zeitg., 1896, p. 187; Bericht d. Bot. 

 Ges., 1897, p. 166; Pfeffer, 1896, I.e., Sect. 20. [Kohl, Bot. Centralbl., Nov. 1897; Gardiner, 

 Phil. Trans., 1883, p. 817.] 



* Zacharias, Flora, 1895, Ergiinzungsband, p. 224. 



5 For other examples of extra-cellular protoplasm, see Schiitt, Die Peridineen, 1895, p. 134 ; 

 Sauvageau, Bot Centralbl., 1890, Bd. XLI, p. 293; Mangin, Recherches anatom. s. 1. composes 

 pectiques, 1893, p. 59. 



